As a conventional vibration environment generator, a technology disclosed in non-patent literature 1 is known. The non-patent literature 1 discloses that in order for the vibration waveform of a vacuum pump to be remotely monitored, the vibration waveforms of 50 samples are observed every 5 seconds by vibration environment power generation using a simple cantilever beam magnetostrictive element and an electromagnetic induction coil. The simple cantilever beam magnetostrictive element is a resonance system which indicates a high Q value at 90 Hz, and an electromagnetic induction coil output of 28 mW at a vibration acceleration of 0.5 g (90 Hz) is obtained. However, since as a wireless communication means for a vibration waveform, IEEE 802.15.4 (ZigBee) is used, power consumption at the time of data transmission is so large as to be about 60 mW. In order to decease the power consumption by the AD conversion of the vibration waveform, unipolar AD conversion is performed without use of an amplifier circuit, with the result that only the +side of the vibration waveform can be monitored and that the −side is converted into zero.
In a simple cantilever beam plate-shaped piezoelectric element mounted on a tire rotary system or the like, since a gravitational acceleration change of G=9.8 m/s2 [0 (vertically downward)→−G (horizontal surface upward)→0 (vertically upward)→+G (horizontal surface downward)→0 (vertically downward)] (in the case of counterclockwise rotation) in a vertical direction per revolution is given, it is possible to expect a relatively large environment power generation power supply. FIG. 1 shows a photograph of a conventional simple cantilever beam piezoelectric generation element and the result of the frequency response evaluation of an output charge at a vertical vibration acceleration of g=0.5 m/s2.
Here, the short-circuit current Is of the piezoelectric generation element is given as:[Formula 1]Is=πfQp√{square root over (3)}  (1)An open voltage Vo is given as:[Formula 2]Vo=Qp/(Co√{square root over (2)})  (2)Here, f is a vibration frequency, Qp is the peak value of the output charge and Co is the capacitance of the piezoelectric element. When the vibration frequency is assumed to be constant, Qp is proportional to the vibration acceleration g.
In FIG. 1, the piezoelectric generation element has a simple cantilever beam structure in which on the beam of SUS (stainless steel plate), PVDF (polyvinylidene fluoride) is formed and in which a weight is loaded at one end. Here, the PVDF has piezoelectric properties. The piezoelectric generation element resonates at 10.44 Hz, and when the vertical vibration acceleration is g=G, a short-circuit current of Is=1064 μArms and an open voltage Vo=182 Vrms are obtained. However, since the vibration acceleration g which can be actually applied at the time of resonance is restricted by the displacement amplitude of the cantilever beam, it is up to about g=G/3. When in non-resonance, the vertical vibration acceleration is g=G, Is=42 μArms and Vo=15 Vrms at f=5 Hz, and Is=53 μArms and Vo=4.7 Vrms at f=20 Hz. Although the matched resistance Zo of the piezoelectric generation element is given as Zo=Vo/Is=1/(2πfCo), and it depends on the vibration frequency f, it is found that in the evaluated element, the vertical vibration acceleration is assumed to be g=G and that thus it is possible to constantly acquire a short-circuit current of 42 μArms or more and an open voltage of 4.7 Vrms or more in the range of the vibration frequency f from 5 Hz to 20 Hz.
FIG. 2 is a block diagram showing the structure of an experimental device invented in the present invention in order to evaluate the conventional simple cantilever beam piezoelectric generation element shown in FIG. 1 and its rotation response power generation amount. In the figure, a charge amplifier converts the output charge of the piezoelectric generation element into a voltage, and performs AD conversion on this voltage with a resolution of 10 bits at a rate of 300 sps. Waveform digital data resulting from the AD conversion is supplied and transmitted, by performing multilevel phase-shift keying (MPSK) modulation on a response subcarrier signal of fs=50 kHz, to a cavity-backed slot antenna for modulation scattering disclosed in patent literature 1. The power consumption of a wireless waveform monitoring terminal which was produced experimentally for verifying this invention is 480 μW including the charge amplifier, and the wireless waveform monitoring terminal is driven by a 3 V coin-type battery (CR 1632). In this experimental device, it is assumed that M=4 (quadrature phase-shift keying), and a signal obtained by performing phase modulation on the response subcarrier signal fs in units of 2-bit information is generated with a subroutine program within a control IC (PIC16F684). A subroutine program which generates, at a code multiplexing rate that is not limited to M=4, phase modulation signals for a plurality of types of response subcarrier frequencies is prepared or the clock frequency of the control IC is changed, and thus it is possible to cope with frequency division multiple access (FDMA) and variable encoding rate communication.
FIG. 3 is a configuration diagram of a receiving device invented in the present invention for a wireless waveform monitoring terminal shown in FIG. 2. In this device, two linearly polarized wave microstrip antennas (V pol. and H pol.) and (0° and 90°) phase shift distributor⋅combiner are used to combine a circularly polarized wave, and thus a inquire carrier CW signal fo is transmitted, and the response MPSK subcarrier signal fo±fs is received. Although an antenna for the wireless waveform monitoring terminal shown in FIG. 2 uses a linearly polarized wave, since the antenna itself is mounted on a rotation system, a polarized wave tilt angel is constantly varied. On the other hand, an antenna on the side of the receiving device shown in FIG. 3 uses a circularly polarized wave, and thus the reception level of a response signal which does not depend on a rotation angle on the side of the wireless waveform monitoring terminal is acquired. Since this reception signal contains a leakage component in the circulator of the inquire carrier signal fo and a reflection component in the antenna, part of the transmitted CW signal fo is subjected to amplitude adjustment and phase reversal such that additive cancellation is performed thereon. The response MPSK subcarrier signal fo±fs received from the wireless waveform monitoring terminal is passed through a RF frequency band limiting filter (2.45±0.5 GHz), is thereafter amplified at the LNA of 20 dB gain, is orthogonally detected by the transmitted CW signal fo, obtains a MPSK subcarrier complex signal ±fs component, is then amplified with a 50-90 dB variable gain amplifier (IF amp), is passed through a switched capacitor (SW-Cap.)±50±5 kHz band pass filter and is thereby subjected to AD conversion at 12 bit/200 ksps. In a DSP for MPSK demodulation (dsPIC33FJ256GP710), discrete Fourier transform (DFT) processing is performed on the complex signal resulting from the AD conversion, only +fs component is detected, an I/Q axis rotation operation for correcting a frequency displacement in the subcarrier signal is performed and then a MPSK demodulation operation corresponding to each information area on I/Q axis coordinates is performed, with the result that it is possible to demodulate the wireless waveform monitoring terminal response signal up to about −110 dBm on the antenna reception level. A unique word for detecting a frequency displacement between a reference phase and the subcarrier signal is attached to the response signal from the wireless waveform monitoring terminal for each bit string packet.
FIG. 4 is an example where the result of an experiment performed with a rotation response wireless waveform monitoring device in the conventional simple cantilever beam piezoelectric vibration generator shown in FIG. 2 is recorded with a receiver shown in FIG. 3. In this graph, with respect to an elapsed time t on the horizontal axis, a piezoelectric element output charge when the number of revolutions is increased and decreased and sweeping is performed is plotted as a waveform on the vertical axis. Around the elapsed time of t=30 seconds, the number of revolutions was 600 rpm, and the piezoelectric element short-circuit current at that time was 19 μArms. This value is about 0.02 times the short-circuit current when the vertical vibration acceleration g=G at a resonant frequency of f=10 Hz shown in FIG. 1. In this case, as compared with gravity, a centrifugal force is significantly exerted. In the case of this experiment, when it is assumed that the rotation radius r of a weight M is 13 cm, the centrifugal force is 512.7 M [N] at 600 rpm whereas the gravity is 9.8 M [N]. This means that a vector exerted on the weight is varied only by about ±1° due to a variation in gravity caused by the rotation, and it can be considered that this is because the resonant vibration displacement amplitude of the piezoelectric element is restricted to 0.02 times. On the other hand, in this figure, the number of revolutions around the elapsed time of t=43 seconds was 300 rpm, and the piezoelectric element short-circuit current at that time was 23 μArms. This value is about 0.55 times the short-circuit current when the vertical vibration acceleration g=G at a nonresonant frequency of f=5 Hz shown in FIG. 1. The number of revolutions around the elapsed time of t=16 seconds was 420 rpm, and the piezoelectric element short-circuit current at that time was 31 μArms. This value is about 0.35 times the short-circuit current when the vertical vibration acceleration g=G at a nonresonant frequency of f=7 Hz shown in FIG. 1. As is found from the observation results, the vibration power generation amount of the conventional simple cantilever beam piezoelectric element by the gravity of the rotation system is significantly reduced by an increase in the centrifugal force.